Shed Structure Foundation Depth Hurricane Area [130 mph] Wind

[RareBugTX]

Hello:

Would like to know if any of you has any experience with structures in hurricane area [Southwest Florida]regarding Fla Building Code requirements for a foundation depth. I am thinking of overturning resistance or uplift forces. Walls to be 4" or 6" reinforced CMU. Owner wants to do only concrete slab on grade. Shed 10'x20'

Any thoughts appreciated.

Rarebug

 

[ron9876]

It depends on various items. The bottom line is it has to be designed not estimated. If you don't have the ability to design the structure I recommend you consult with a structural engineer.

 

[RareBugTX]

Thats not a thought, maybe a egotist rant! Please disregard and move on to the next thread!

 

[JAE]

RareBugRA,
I have to confess limited knowledge of the Florida code in particular (Ron are you out there?), but in general, a flat mat foundation might work as long as you check the 0.6D + W uplift combination and verify that the slab is stiff enough to account for loading on the portion that would participate in holding down the load bearing walls or columns.

A thin slab, getting pulled up by its edges, may not have enough dead weight tributary to the walls to work. The amount of slab you use as tributary to the walls would depend on the slab stiffness.

General comments but I'd need to see the actual code language to help you any more than that. Perhaps others out there - anyone?

 

[RareBugTX]

Jae: thanks for your constructive comment. More than enough to work it out.

Regards!

 

[Ron]

RareBugRA...agree with JAE on the technical. Slab on grade with sufficient consideration for uplift/overturning should work fine. In the event that the geometry of the building presents an issue with overturning, you can supplement the slab with tie-downs such as helical soil anchors; however, depending on where you are in south Florida, you might be sitting almost on "rock", so that might be ineffective.

The foundation/slab must also be designed for lateral bearing/movement. This is to determine the minimum depth of the foundation, based on lateral sliding resistance.

As for the depth of foundation for vertical loads according to the Florida Building Code....for monolithic slab/foundation systems, the minimum depth is 12 inches....but you still have to check for sliding.

A 4-inch masonry wall might give you a bit of a problem under the wind loads in that area. You will be limited to a wall height of less than 7 feet for a 4" bearing wall.

Also, ...no need to be snarky. Ron9876 gave you good advice if you are not a structural engineer; and presumably you're not since you asked these questions. We commonly get contractors asking such questions hoping to save some money....keep in mind that the building department will require signed/sealed drawings and in some cases, calculations. For these reasons, Ron9876's comment was right on target.

Now be nice and apologize!

 

[RareBugTX]

Thanks Ron forthe time you took to highlight these items. By the way, City in this jurisdiction does not require stamped plans not to mention calculations. They even have "standard" details for homeowners to reproduce at their discretion and get easy permits. I find them questionable. It is tiny shed the subject structure. Anyhow i do not believe used foul language but here it goes the apology If anybody was offended to keep the bytes cordial. I attended engineering school and will be sitting for PE examination this year but do not think i'll ever stop learning from fine people like you .Regards!

 

[msquared48]

Thank you for that. Best wishes for your exam.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Ron]

RareBugRA...good luck with the exam.

Didn't realize this was a residential shed. Requirements are less for the slab edge. Can do 8" depth for utility shed, particularly if less than 450 sf. Still need to check for sliding, overturning and other high wind considerations.

Geez...now we have a municipality practicing engineering without a license!!

 

[MiketheEngineer]

Without knowing the exact dimensions of your building, roof pitch, importance factor and exposure, etc, etc - I would guess the uplift somewhere in the 15-20 psf range.

Design for that.

 

[steellion]

I would also add that reinforcing a 6" CMU wall is difficult and reinforcing a 4" wall is near-impossible.

 

[msquared48]

Saw a lot of unreinforced 8" CMU laying on the ground in some of the videos and pictures of the devastation in Kentucky.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JedClampett]

I've done some work in Florida. It's not my wheelhouse, however. As a matter of fact I'm sitting in a hotel room in West Palm Beach right now.
But I think most failures occur well above the concrete slab, not within it. Or maybe the attachment to the slab. If concrete is good at nothing else, it provides a lot of mass for very little money. With enough reinforcing to activate the mass, you can at least move on to the next weak link. Run the overturning and sliding numbers and see what kind of slab you need. But I suspect that other things will control.

 

[RareBugTX]

Jed:
Thanks for your valuable input!. Initially, I was exactly thinking on the sliding and overturning resistance, but was curious how the foundation depth component played in all these.

It would be worthless to figure out steel anchoring to the slab or foundation wall or detail the roofing attachment to the wall,and have the building roll over altogeter, and I think the foundation depth plays an important role in both sliding and overturning resistance.

Thanks!

 

[concretemasonry]

A 4" reinforced block is usually impossible. A 6" reinforced wall can be a piece of cake with modern masonry units. Unfortunately, most of the 6" units made in Florida are not really produced for reinforced masonry because of the habit of using 8" thick old fashioned units. The 8" units there are "cookie cutter" designs without much regard to use.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.